[Programmatic]

The AK in particular is an interesting weapon in that the controlled part (legislation around guns deals with the concrete part that "is" the firearm, which is the action that houses nearly all of the other parts) is made out of stamped/bent sheet metal.

The harder part in the case of an AK is the parts kit that has all of the other parts that must be actually machined. Step 0 of making an AK from a shovel is "buy a parts kit made from an entire old, previously functional gun minus the sheet metal and wooden furniture". In terms of making a true firearm from scratch an AK would still be fairly difficult. In terms of making a technical "firearm" (the controlled part), the AK is one of the simplest.